Aluminum alloys



Patented Oct. 31, 1933 UNITED STATES PATENT OFFIE Ohio,

Pennsylvania No Drawing.

assignors to Aluminum Company of America, Pittsburgh,

Pa., a corporation of Application September 21, 1932 Serial No. 634,163

2 Claims.

This invention relates to aluminum base alloys and has as its principal object the provision of alloys which may be readily cast into permanent molds to produce comparatively light strong castings capable of retaining a substantial proportion of their strength and elongation at elevated temperatures. A further object of the invention is the provision of a casting alloy which may be used in either sand or permanent mold foundry to produce such castings as require a high surface finish and a good resistance to corrosion.

The aluminum base alloys containing magnesium are extremely light and are likewise strong. Such alloys, however, do not, in binary form, meet all of the requirements of a good foundry alloy. Moreover, light alloy castings are in demand for use as reciprocating parts which operate at elevated temperatures and the binary aluminum-magnesium alloys do not have, in many instances, the properties desired at high temperatures.

We have discovered that the properties of certain of the binary aluminum-magnesium alloys may be substantially improved by the addition thereto of certain limited amounts of nickel. The presence of nickel in the alloy is more efficient, we have discovered, in maintaining the original ductility of the alloy at high temperature than any other alloying element to us known. The nickel improves the strength of the alloy at elevated temperatures without affecting its ductility to as large an extent as do the other hardening elements. In experimenting with such alloys we have discovered that those alloys containing 3.0 to 7.5 per cent by weight of magnesium and 0.2 to 2.0 per cent by weight of nickel, the balance being principally aluminum, are peculiarly adapted to use at high temperatures and offer, for that purpose, a combination of lightness, strength and ductility seldom encountered in structural material. We have, moreover, found that these alloys have excellent foundry characteristics and can be used in the production of intricate castings. While particularly adapted to the manufacture of permanent mold castings, the alloys are likewise amenable to casting in sand molds and can, therefore, be used in an all-purpose foundry with considerable success.

When the alloys are cast into permanent molds, we prefer to use a somewhat narrower composition range, the preferred alloys for this purpose containing 3.5 to 4.5 per cent by weight of magnesium and 0.25 to 1.0 per cent by weight a lasting polished surface.

The high temperature properties of our novel alloys are excellent. For instance, an alloy containing 6.0 per cent by weight of magnesium, the balance being principally aluminum, in sand cast form after heating for 4 hours at 700 7 Fahrenheit and then 20 days at 600 Fahrenheit had, at that temperature, a tensile strength of 15,000 pounds per square inch and an elongation of 5 per cent in 2 inches. A similar alloy,

similarly treated but containing 1.5 per cent of nickel, had a tensile strength of 17,000 pounds per square inch and an elongation of 7.2 per cent in 2 inches. Thus it will be seen that the addition of nickel to the alloy has raised the tensile strength at high temperature and has not decreased the elongation but has, in fact, increased it. These properties of the alloys, together with their light weight, are extremely useful.

In further experimenting with these alloys, we have discovered that the addition thereto of a very small amount of a class of elements herein defined to be antimony and bismuth will increase both strength and ductility at elevated temperatures. or bismuth which may be added is extremely limited, the amount being 0.05 to 0.4 per cent by weight of the total alloy. If added in amounts greater than about 0.4 per cent, the effect is reversed and the elongation of the alloy is reduced. Either antimony or bismuth or both metals may be used but in total they should not exceed about 0.4 per cent. Bismuth, we have found, is somewhat more efiicient than is antimony, but either or both are satisfactory.

The alloys of our invention may be compounded in the usual fashion by melting the aluminum and adding thereto the other metals either singly or in alloy form. Likewise any other commercial method of alloying will be material for parts operating at elevated tem- The amount of antimony 0 peratures. Comparative tests, based upon the distance that the molten alloy, originally heated to a given temperature, will flow through a spiral formed in a sand mold, have shown that our novel alloys are very superior with respect to fluidity.

The aluminum used in the manufacture of the alloys may be of the highest purity or it may containamounts of usual impurities, and the term aluminum as used herein and in the claims designates the aluminum of commerce. It is an incidental property of our alloys that the presence of iron in amounts as high as 2 per cent by weight is not harmful to the high temperature properties of the alloys and, therefore, a wide choice between the various grades of commercial aluminum is possible.

We claim:

1. A metallic alloy characterized by high physical and tensile properties at elevated temperatures and good fluidity and consisting of 3.0 to 7.5 per cent by weight of magnesium, 0.2 to 2.0 per cent by weight of nickel, and 0.05 to 0.4 per cent by weight of at least one of the class of elements antimony and bismuth, the total amount of the antimony and/or bismuth being not greater than 0.4 per cent by weight, the balance of the alloy being aluminum.

2. A metallic alloy characterized by high physical and tensile properties at elevated temperatures and good fluidity and consisting of 3.5 to 4.5 per cent by weight of magnesium, 0.25 to 1.0 per cent by weight of nickel, and 0.05 to 0.4 per cent by weight of at least one of the class of elements antimony and bismuth, the total amount of the antimony and/or hismuth being not greater than 0.4 per cent by weight, the balance of the alloy being aluminum.

WALTER A. DEAN. LOUIS 'W. KEMIPF. 

